Bandwidth in wireline communication systems such as those based on the T1/E1 and DSL data transmission technologies can be increased by bonding (i.e. aggregating) several physical communication lines together to form a single logical link having a higher combined bandwidth. A bonding group includes a bidirectional data stream transported by multiple bidirectional bearers across multiple physical media in both upstream and downstream directions, e.g., between CPE (customer premise equipment) and CO (central office) entities.
On the transmitter side, outgoing data packets are disassembled into fragments and spread over a plurality of communication lines using a bonding protocol (e.g. a round robin method). For example, one packet fragment can be assigned to a first bonding line, a second fragment to a different line and so on. The packet fragments are transmitted over the bonding lines in a particular sequence. The receiver monitors the bonding lines for newly transmitted packet fragments and reassembles the packet data from recovered packet fragments. A sequence ID (SID) is included with each transmitted packet fragment to indicate the order in which the different fragments occur within a packet so that the packet can be properly reassembled.
However, not all packet fragments are transmitted without error. For example, noise or interference can cause data transmission errors on one or more of the bonded communication lines. The receiver requests retransmission of each erroneous packet fragment via the bonding line that caused the transmission error. Packet fragments continue to arrive on the bonding lines not affected by the transmission error. These valid packet fragments are recovered and used for packet reassembly. Care must be taken by the receiver to not process packet fragments out of order while waiting for retransmission of older packet fragments. Also, only a small amount of buffer capacity is typically available to support bonding and packet reassembly functions at the receiver. The bonding and packet reassembly buffer at the receiver can quickly overflow while the receiver waits for retransmission of older packet fragments. In each case, packet data can be lost or corrupted when data transmissions errors occur in a wireline communication system that employs both packet fragment retransmission and channel bonding.